Recent years have seen the development of biometric authentication technology for authenticating a user of an apparatus or system based on a biometric image representing the user's biometric information such as a palm or finger vein pattern or a fingerprint or palm print. A biometric authentication apparatus using such biometric authentication technology acquires, for example, as an input biometric image, a biometric image representing the biometric information of the user who is going to use the biometric authentication apparatus. Then, the biometric authentication apparatus compares input biometric information, i.e., the user's biometric information represented on the input biometric image, with preregistered biometric information, i.e., the biometric information prestored in the form of a biometric image for each preregistered user. If the result of the comparison indicates that the input biometric information matches the preregistered biometric information, the biometric authentication apparatus authenticates the user as being a legitimate registered user. The biometric authentication apparatus then permits the authenticated user to use the apparatus in which the biometric authentication apparatus is incorporated or some other apparatus connected to the biometric authentication apparatus.
The biometric information represented on such a biometric image changes depending on the condition at the time of acquisition of the biometric image. For example, when a palm vein pattern is used for authentication, the condition at the time of biometric image acquisition that affects the biometric information includes the orientation of the hand such as the position or tilting of the hand relative to the vein sensor. On the other hand, when a fingerprint is used for authentication, the condition at the time of biometric image acquisition that affects the biometric information includes the orientation of the finger relative to an area-type fingerprint sensor or the moving speed of the finger relative to a slide-type fingerprint sensor. If the change in the biometric information is large enough that the difference between the input biometric information represented on the input biometric image and the preregistered biometric information represented on the biometric image acquired at the time of registration becomes significant, the authentication accuracy may degrade. In view of this, the biometric authentication apparatus, for example, determines whether the condition at the time of acquisition of the biometric image is appropriate or not, and if it is determined that the condition is not appropriate, an image of the biometric pattern is recaptured to reacquire the biometric image, and the reacquired biometric image is used for authentication, thereby preventing the degradation of the authentication accuracy.
The biometric information represented on the biometric image may also change when the condition of the body part containing the biometric information is affected, for example, by an environmental factor such as weather. When a palm vein pattern is used for authentication, the condition of the body part is, for example, the degree of contraction of the blood vessels due to temperature. On the other hand, when a fingerprint is used for authentication, the condition of the body part is, for example, the skin condition which depends on the degree of dryness of the skin surface due to humidity. For most users, the condition of the body part containing the biometric information is relatively unaffected by temperature or humidity variations associated with seasonal variations; therefore, for such users, the authentication accuracy is stable throughout the year.
On the other hand, for some users, the condition of the body part containing the biometric information may be significantly affected by temperature or humidity variations associated with seasonal variations. For such users, if the biometric information is registered, for example, in summer, the input biometric information represented on the input biometric image acquired in winter for authentication may be significantly different from the registered biometric information, and the biometric authentication apparatus may fail to authenticate the user.
In the prior art, methods are proposed for updating the registered biometric information as needed (for example, refer to Japanese Laid-open Patent Publication Nos. 2007-226519, 2010-61528, 2006-85268, 2010-79448, and 2008-171094). For example, in Japanese Laid-open Patent Publication No. 2007-226519, there is proposed a biometric information updating management system in which, if the last update date of the master biometric information stored in a storage device is past its validity date, the biometric information presented for authentication and judged to match the master biometric information is registered as the master biometric information. On the other hand, in Japanese Laid-open Patent Publication No. 2010-61528, there is disclosed a biometric authentication apparatus in which feature information having high reproducibility is extracted from the registered data and the data presented for authentication, and new registration data is created from the extracted feature information and is used to update the registered data.
Further, in Japanese Laid-open Patent Publication No. 2006-85268, there is proposed a biometric authentication system in which when the performance of authentication using the registered data stored in an IC card registration data storage unit has degraded, the registered data stored in the registration data storage unit is updated by registered data stored in a registration database. Furthermore, in Japanese Laid-open Patent Publication No. 2010-79448, there is proposed a finger vein authentication system which determines whether the preregistered finger vein pattern data is appropriate or not, and urges the user to perform a re-registration operation depending on the result of the determination. On the other hand, in Japanese Laid-open Patent Publication No. 2008-171094, there is disclosed a biometric authentication apparatus which determines whether the biometric information presented for authentication is to be accepted or not, based on the matching score between the presented biometric information and each one of a plurality of biometric information templates, in order to replace a selected one of the biometric information templates with the accepted biometric information.
However, in any of these prior art methods, the registered biometric information is updated independently of cyclic environmental variations such as seasonal variations. Therefore, there can occur cases where the registered biometric information representing the condition of the body part containing the biometric information acquired in a given season, for example, is updated by the biometric information acquired in a different season. As a result, if authentication is performed after a certain length of period has elapsed from the last update of the registered biometric information, since the season at the time of the authentication is different from the season at the time of the registration, it follows that the biometric authentication apparatus performs the authentication by using the registered biometric information representing the condition that is different from the condition of the body part at the time of the authentication. This can result in a degradation of authentication accuracy.
On the other hand, there is proposed a fingerprint matching system in which date/time information such as the time of day, day of week, and date of year of registration is registered along with each fingerprint image and, at the time of fingerprint matching, fingerprint images registered within a specified date/time range are read out and used for matching (for example, refer to Japanese Laid-open Patent Publication No. 2001-229380).